Not necessarily. You can go to the PG website and request an invite.
They MAY have changed their policy, but in 2004 (June) I contacted PG and received the invite for the SE Underclass held at Duke back in August, 2004.
I spoke with Jim Arp live at PG and discussed with him what made the most sense for my son (discussed ability, travel teams he had played, as well as dates/logistics of events that worked for our family).
ALL of my dealings with PG have been very positive. I have found them to be candid, honest and helpful every time I have had to contact them.
Feel free to send me a PM if you would like further details.